/holiday174-star

Minimalist Computing - Holiday174 Design Contest - Blinking Star

CERN Open Hardware Licence Version 2 - Strongly ReciprocalCERN-OHL-S-2.0

Minimalist Computing - Holiday Design Contest

This project is my submission for the Facebook's Minimalist Computing group Holiday Design Contest.

Design Contest Rules

  • Holiday related design
  • Can use one 7400-series IC. The logic family does not matter. It can be HC, LS, etc.
  • Can use 2 transistors maximum
  • Any number of passive components: capacitors, resistors, diodes, coils, LEDs (without any ICs in the LED packages, e.g. self-flashing or color changing LEDs)
  • The only external connection is the power supply

My Design's Description

My design is an eight pointed star with animated LEDs. The shape is inspired by the Vintage Computing Christmas Challenge 2022.

The design includes:

  • A multivibrator, implemented using two transistors - Q1 and Q2, four resistors - R50-R53, and two capacitors - C2 and C3. The multivibrator provides the clock for the rest of the circuit.
    • The choosen values of the R52, R53 - 62 k, C2 and C3 - 2.2 uF result in approximately 5.3 Hz frequency.
    • The formula to calculate the frequency is f = 1 / (ln(2)(R52*C2+R53*C3)), or since R52 = R53 and C2 = C3, it can be simplifed to f ~= 0.72/(R52*C2).
  • A 4 bit Johnson counter, implemented using a 74*175 - four D-type flip-flops IC.
    • In my own build I used the 74LS175 IC, but I think any other series will work just as well.
  • 3 outputs of the counter are connected to the LEDs through current limiting resistors. The last output is not connected to the LEDs. This doubles the delay when all LEDs are on and when all LEDs are off.
    • The LEDs are connected between the inverted outputs of the flip-flops and VCC. This is because TTL/TTL-LS series ICs have the low-level output current IOL much higher than the high-level output current IOH. For the 74LS175 the values are 16 mA and -800 uA respectively.
    • The current limiting resistors have a fairly large resistance. I used 4.7 k for red LEDs and 10k for green and blue LEDs. This keeps the current well within the IC's IOL specifications.

Star Assembled Board

Design Files

Licensing

The hardware design, including schematic and PCB layout design files are licensed under the strongly-reciprocal variant of CERN Open Hardware Licence version 2.